1. Field of the Invention
The present invention relates to coating compositions containing fluorescent colorants, more particularly, to coating compositions containing reflective pigments and colorants which absorb visible light in a first wavelength band and produce fluorescent light at a second wavelength band when exposed to visible light.
2. Prior Art
Colored coating compositions typically include colorant particles dispersed in a resinous binder. The coating composition may further include reflective pigments, such as aluminum flake or metal oxide coated mica or other color effect pigment compositions or substrate-hiding materials, such as titanium dioxide. Conventional automotive solid-colored coatings include a resin and colored pigments which determine the desired coloration of the coating. Typically, solid color pigments are of a size such that they will scatter incident light effectively. The scattering will be in all directions.
Conventionally, in a pigmented coating composition, light that is scattered back out of the coating is described as being diffusely reflected while light that is scattered forwards through the coating composition is described as diffuse transmission. This scattering, in particular diffuse reflectance, is often desirable, providing opacity to the coating and hiding the surface of a coated article. Solid color pigments also typically absorb a portion of the incident light such that the light that is diffusely scattered and the remainder that is diffusely transmitted has a perceived color. Typically, this perceived color does not vary greatly with viewing angle. For those coating compositions that further include reflective pigments, such as aluminum flake or metal oxide coated mica or other color effect pigment compositions, the portion of the incident light that is not absorbed or diffusely reflected by the colored pigment will interact with these color effect pigments. This portion of incident light may be specularly reflected by aluminum flake, or may interact with the coated mica or other effect pigment to produce a reflection whose perceived color is influenced by the structure of the pigment via an interference phenomenon. If this portion is specularly reflected by aluminum flake, there may be a perceived change in the color of the coating composition, typically described as flop. The perceived color will appear bright at viewing angles close to specular (on face), and appear to darken at viewing angles far from specular (on flop). If this portion undergoes interference on interaction with coated mica flake, there may also be a perceived change in the color of the coating composition, typically in hue as well as lightness or darkness. This viewing angle-dependent colored appearance of the coated surface produces color effects which are perceived positively by customers as being highly desirable, particularly as styling tools in automotive coatings.
Angle-dependent color effect pigments that result in hue changes (goniochromatic pigments) typically are interference pigments, such as mica pigments coated with a metal oxide. Interference pigments can be complex to prepare and are costly to include in a color effect coating composition.
Accordingly, a need remains for a coating composition having an angle-dependent color effect which may be produced cost effectively.